After two hours zinc oxide sunscreen loses effectiveness, becomes toxic: study | Hacker News Reader

After two hours zinc oxide sunscreen loses effectiveness, becomes toxic: study

phys.org

127 pointsXzetaU881 comments

Putting together all the messaging I've gotten recently: Regular sunscreen is bad, zinc oxide sunscreen is bad, getting sun is bad, not getting sun is bad (Vitamin D).

I realize you're being a bit humorous, but it's true 'the messaging' on this can be muddled.

"getting sun is bad" should be strictly "too much UV exposure over a long period of time is bad" which is currently unambiguously what the evidence demonstrates.

I have also started to avoid sunscreens and wear synthetic fabrics instead which aggressively filter out UV light, or I schedule fewer outdoors-in-direct-sun activities during peak UV hours when I have that option.

Burning your skin is also really bad though, any amount of UV will also reduce the ability of your skin to properly regenerate and heal for a few days.

There is no threshold for harm*. It's a cost:benefit consideration. From a cancer/aging perspective, any amount of UV exposure is bad. Tanning is a consequence of DNA damage. If your skin gets darker from sun exposure, you see evidence of your skin cells reacting to increased DNA repair signals. Malignant transformation/senescence is a stochastic event of course, but age markers pretty much suffer in a dose dependent manner.

* Of course exhausting antioxidant capacity will greatly increase damage at a certain point. I am not exactly sure if UV light can cause single strand breakage by itself, or via ROS, but antioxidants are no "shield" in any case - more like a minefield.

The antidote for damage from UV light is the pro-metabolic effects of red light. Red light hits the red metal (copper) in the Cytochrome C Oxidase enzyme [0] in our mitochondria and refreshes this enzyme. When the cells have enough energy (ATP) they can repair the damage from UV light.

[0] https://en.wikipedia.org/wiki/Cytochrome_c_oxidase (no mention of red light therapy in this article).

UV light from the sun comes with plenty of red light. UV light from the tanning bed does not have any red light. In the winter I used to go tanning, then would spend 12 minutes in the bright-light room [1].

[1] at Planet Fitness. The company website doesn't have any information, but I found this page: https://thelifevirtue.com/total-body-enhancement-pros-and-co...

This explains the therapeutic benefits of red light on retinal tissue.

I was curious so performed a brief search. What are your thoughts on this study, which suggests that cytochrome c oxidase is not involved in the effect?: https://doi.org/10.1016/j.jphotobiol.2019.03.015

I think your link is interesting, in that the group without the copper enzyme also benefited from red light exposure. The copper enzyme explanation seemed reasonable to me, but perhaps there’s better explanation for why people seem to benefit from red light exposure. Maybe the benefit from red light it multifaceted.

Getting sun is awesome. Just be reasonable and dont over expose yourself, especially mid day sun. The key is moderate, daily exposure of skin without lotions on it blocking it. Your skin will adapt as the seasons change, you will have stronger immune systems, better mood, etc.

Being pale and then going for 4 hours at noon to the beach is trouble, build up to it or wear clothing to shade you. If you are naturally pasty and live in the tropics.. mmm . You are in trouble.

I believe mid day sun is the best for producing vitamin d though.

Correct, the atmosphere will block the rays that cause vitamin d production so the best time to be exposed is around noon +/- a few hours when the sun is above you

Australasia has it particularly bad. I have fair skin — 20 min in the sun on a boat with no sunscreen a few summers ago and I had a series of doctors visits over the next week to treat the, quite literally, blistering sunburn.

Someone told me that I will die of something. Crazy talk.

You can't outsmart entropy!

Indeed. You started dying the moment you were born!

sounds like "eggs" and "good vs bad cholesterol" all over again

Not really, it's more just that there's no perfect, general, choice, a lot of unknowns and a decent amount of nuance about what _is_ known.

Also with eggs and cholesterol

With eggs it's pretty much: eat them if you like eggs :shrug:

With the Sun... you're already exposing yourself to a giant irradiating ball of fire, but also our bodies are evolved to require some exposure to produce vitD. How much exposure should you get? Nobody really knows. Should you wear sunscreen, or just moderate exposure? Which sunscreen? What good choices are there? It's all a mess.

This is how I feel a lot of health "news" works. I'm pretty hesitant to start eating "better" because everyone, even so-called experts in the field, seem to have not just differing, but oftentimes polar opposite opinions or guidance about things.

It is so insanely hard to filter the truth from the lies when it comes to this stuff.

I don't think there's any real debate that eating whole, unprocessed foods, mostly plants, is the best thing you can do for your diet.

What are your qualifications?

Of course there is. There are people that think eating only red meat is the best diet.

I also don't believe that eating "mostly plants" is the best way of eating healthy.

That's a good enough default stance, but reality is more complicated. I'll list a couple of points, and in general there are many scenarios where more heavily processed foods are advantageous, and to a lesser degree I think some people would benefit from a high percentage of calories coming from meat and fish.

- Most plants are a little dangerous to consume raw in significant quantities, especially over any extended period of time, especially if you're one of the 15% of the US with kidney issues, especially if you're one of the 1% of the US with IBD, etc. If your diet is mostly plants, the processing you do should at a minimum include cooking most of them for a few minutes. Some vitamins will be destroyed, but that's a preferable outcome.

- If you have any kind of nutrient deficiency (e.g., calcium is a common issue) and want to solve the issue with your diet, you'll typically want to choose foods that have been processed to be easier to digest and/or to be fortified with such a nutrient. For calcium in particular a diet consisting mostly of unprocessed plants is insufficient.

- Some foods (tomatoes are a classic example) have higher nutritional value when bought cooked and canned than when bought "fresh" because the canned product was produced with much fresher ingredients.

- The majority of the US lives paycheck to paycheck. There's an economic argument to be made that heavily processed foods can be preferable to the alternatives if they allow you to get your vegetables and other nutrition more cheaply (both in direct cost savings and also in the ability to buy in bulk without spoilage).

- Not everyone has the same health goals or personal chemistry, and a linearizable ordering doesn't exist for many diet choices that would apply to every individual across time. For a few choice examples, (1) roughly 1% of the population are underweight and benefit from diet choices enabling weight gain (i.e., on average probably not the proposed diet), and (2) a mostly different 1% subset with IBD benefits from the immunosuppressive effects of low to moderate alcohol consumption even despite its other negative effects (that point is still being studied/debated -- alcohol affects some individuals in that group more negatively than others, talk to your doctor).

If you preface each of your statements with "too much", then suddenly all 4 can make sense and be useful.

What a horrible article, repeating the ever same superficial factoid in variation, without ever adding more info.

So apparently zinc oxide acts as a catalyst, which reacts with some sunscreen ingredients to form substances toxic to zebra fish, under laboratory conditions.

No qualitative analysis of what's reacting with what? Which substances make the toxicity? Hardly worth anyone's time at that point no?

Came here to say the same thing. I would have expected at least a small amount of chemical analysis. Something more than “toxic to zebra fish”. Also some information about how toxicity was measured like how much sunscreen the fish were exposed to, what effects it had on them.

It's not horrible just because it cannot answer all your questions. The article summarizes a research paper and provides a link for all the raw details.

As someone with a severe photosensitivity disorder, I have relied on zinc oxide as a "physical" blocker as opposed to various chemicals that often seem to be banned in the EU.

But digging into the article, which is a little short on specifics, it appears that the zinc oxide is catalyzing a reaction with the "organic" compounds which also are blockers. Zinc oxide is already a pretty good UVA blocker, especially with a smaller particulate size. My guess is that this is for sunscreens with a mix of organic UVA blockers and zinc oxide, but not so much zinc oxide that you look like you are training for mime school.

My preferred (aka "least objectionable") blend is only zinc oxide, so I may not have to worry.

I wish I had access to a UV-VIS spectrophotometer and various defined particle sizes of zinc oxide and titanium dioxide. My suspicion is that a careful formulation -- probably arrived at via linear algebra -- of different particle sizes should allow for a sunscreen that almost has a step function at around 410 nanometers: invisible at longer wavelengths, a complete block at anything shorter than 410 nm. This way, one could avoid the ghost whiteness.

It's easy enough to make your own cosmetics these days. You might look into it.

I have, but again, it's the UV-VIS spectrophotometer access that I need.

Would be cool if there was a "maker lab" somewhere with these tools.

> made five mixtures containing the UV filters—the active ingredients in sunscreens—from different products available in the United States and Europe. They also made additional mixtures with the same ingredients, plus zinc oxide at the lower end of the commercially recommended amount.

This sounds like they made mixtures of the usual chemical sunscreens that people already have concerns about, then added zinc to the mixture and found it caused the chemical sunscreens to degrade more.

That’s an important finding but what about the pure mineral sunblocks that don’t have any of the chemical sunscreens.

It looks like the FDA puts safety limits on what percentage of each blocking chemical can be put in sunscreen but allows mixing the maximum allowed of each (I presume to achieve higher SPF?). This study might be looking into this.

> (a) Aminobenzoic acid (PABA) up to 15 percent. (b) Avobenzone up to 3 percent. (c) Cinoxate up to 3 percent. (d) Dioxybenzone up to 3 percent. (e) Ensulizole8 up to 4 percent. (f) Homosalate up to 15 percent. (g) Meradimate9 up to 5 percent. (h) Octinoxate10 up to 7.5 percent. (i) Octisalate11 up to 5 percent. (j) Octocrylene up to 10 percent. (k) Oxybenzone up to 6 percent. (l) Padimate O up to 8 percent. (m) Sulisobenzone up to 10 percent. (n) Titanium dioxide up to 25 percent. (o) Trolamine salicylate up to 12 percent. (p) Zinc oxide up to 25 percent.

> "(1) Two or more sunscreen active ingredients identified in §§ M020.10(a), (c), (d), (e), (f), and (g) through (p) may be combined with each other in a single product when used in the concentrations established for each ingredient in § M020.10. The concentration of each active ingredient must be sufficient to contribute a minimum SPF of not less than 2 to the finished product. The finished product must have a minimum SPF of not less than the number of sunscreen active ingredients used in the combination multiplied by 2." [1]

[1] https://www.accessdata.fda.gov/scripts/cder/omuf/index.cfm?e...

Does anyone know why Zinc oxide and Titanium oxide are limited to 25%? The linked document doesn't provide any reasons.

This makes no sense. Both substances are in FDA's list of generally recognized as safe, or GRAS, substances, meaning: you can eat them safely.

Maybe I'm missing something, but it seems like this study only examined mixtures of organic UV absorbers +/- Zn/Ti and did not examine the inorganic UV absorbers alone. But my understanding was that most sunscreens are exclusively organic or inorganic, so such mixtures don't happen unless one mixes different sunscreens. Does this study actually have much real world relevance?

Also I would hope that nobody makes combined sunscreens - metal catalyzed photodegradation is well known and anyway cosmetic/drug products should be getting photostability studies as part of routine development. Naively one would think organic UV absorbers would be especially liable to interactions because they're all huge conjugated systems hanging around in excited states, but maybe fragrances / unsaturated fatty acids do it too. In any case studying mineral-only formulations would have been nice to see.

It sounds like they got some commercially available chemical sunscreens and added zinc oxide, which caused a reaction in those components, increasing their toxicity. That seems bad, but in my experience, zinc oxide is used in lieu of chemical components, not in addition to them. I'm not clear this interpretation is correct because the article only mentions zinc oxide, not the components which reacted to it.

Yeah the study has that major flaw. There are actually a lot of chemical sunscreens where they throw in a few % of zinc oxide for whatever reason, so it’s important to study but these aren’t billed as “natural” or safer. it’s a very flawed study not to test the pure mineral sunscreens.

It's not even clear that they did that. It sounds like they made their own sunscreens from the ingredients commonly found in some sunscreens and then added the zinc oxide to test what would happen.

So I live most of the time in Costa Rica, and a lot of the surfers here actually just use pretty much straight zinc oxide diaper rash cream (We call it "Pañalito" which means little diaper) and when you have it all over your face you look like a ghost for a bit. They prefer it because it's WAY cheaper than sunscreen on the beach (They charge it like 20$+ for a bottle to get tourists who just unflinchingly pay that kind of price), so I actually spend a lot of time wondering about the topic in this link. My concern is a lot around the effect this may have on the environment, because they're probably the people who are spending the most time out in the ocean. We all talk like it's better for the fish somehow but this study might be evidence to contradict that.

I could not immediately tell from the published research what sunscreen alternatives are a better choice. Seems the general advice is to avoid sunscreen containing both zinc and titanium oxide. Apparently the EU has a lot of options to choose from, and while there are fewer options in the US.

That's interesting because those ingredients are "physical" sunscreens which have been gaining popularity in some part because of concerns over health and environmental impacts of many chemical sunscreens (significant absorption through the skin and subsequently detectable levels in blood possibly leading to hormone disruption and destructive to coral and sea life health)

The headline is misleading @dang. The study did not show the sunscreen becomes toxic to humans:

> the zinc-oxide-induced photodegradation products caused significant increases in defects to the zebrafish we used to test toxicity. That suggests zinc oxide particles are leading to degradants whose introduction to aquatic ecosystems is environmentally hazardous."

@dang has no effect and doesn’t email the mods or trigger attention to your mod concerns. If it ever looks like it’s worked, it’s either because someone emailed the mods for you or because they tripped over your comment by accident. If you want to email the mods, use the footer Contact link to do so instead of a comment.

"to zebrafish" should be added to the headline. This amount of zinc does not harm you.

I am still amazed mankind survived all these millennia without sunscreen. How can that be?

Nearly everyone's skin color/melanin-level was adapted to where they were born.

Dark skin gives you some protection from sun, but not nearly enough - somewhere around SPF 10 IIRC.

Increased melanin level helped, but didn’t solve the problem. It’s evolution driven, so it gave people living in more sunny places enough of protection, so they can reproduce.

Except East Asians, who according to my information (...I couldn't find a reference quickly) descended not-so-long ago from something like Inuit or Siberians. At least they can get tanned, it seems, as easily or better than Central Europeans.

Dying before you grow old enough to get cancer does the trick. Remember to reproduce before that.

People lived up to reasonable ages if they reached adolescence.

The idea that everybody died young is a myth.

Not on average, the odds of living to be 70 where quite low in primitive societies compared to today. That said sure some people live to be 90+.

Ancient Rome gives you something like a life expectancy of 50 years if you survived being a baby.

But I also think ancient Romans would not lay in a tanning booth, or be indoors for 10 months and then take a 7 day trip to Mexico and burn to a crisp on the beach.

Also, 50 is pretty young. Skin cancer would probably not get most people before they were 50, even with a lot of sun exposure. I bet some did die of skin cancer younger than 50, too.

MRNA treatments should be able to handle this soonish.

This doesn't seem connected to the question of how people historically have avoided dying of skin cancer?

Today, the average age of Melanoma diagnosis is 63, so they very well may have still died by large before typical onset.

https://www.curemelanoma.org/about-melanoma/melanoma-statist...

This. Thanks.

Maybe we didn't! I recall reading about Egyptians using jasmine and rice-based sunscreen.

We survived winters without fur. Perhaps sunscreen isn't much different. Mud slathered on our bodies to avoid painful sunburns in Summer could've worked fine for 300,000 years just as animal hide and straw worked to avoid freezing to death in Winter.

But there may be more to it. I wonder if the intensity of the Sun and/or the strength of Earth's magnetic field could fluctuate more than current science has been able to determine.

Also all kind of hats and clothing to protect from the sun. Desert dwellers wrapped themselves as best as they could.

because after a few weeks at the beginning of summer getting horrific burns you would tan enough for it to stop being too bad (and the eventual skin cancer would historically be the least of your concerns)

Skin cancer typically hits way after the age that most people have kids

I love reading all the speculative answers you're getting. Can anyone give something more solid? Like maybe an anthropoligist's POV?

I will give my own : I believe skin cancer and hayfever are diseases of 'modernity' ( I don't have the proper English term right now ). Office life.

If I just go outside often enough as soon as it is nice ( March, April ), I get no sunburn nor hayfever.

Given that animals can also get skin cancer from excessive sun exposure, I think your basis for this belief is flawed.

Also not burning in the sun doesn't indicate anything, not everyone gets sunburn and it doesn't mean your skin cells DNA are not being damanged and increasing the chance of cancer.

Prehaps more relevant to modern life is the ozone layer was vastly stronger in the past which filtered out the damaging frequencies.

Stay out the sun!

I always hear this about allergies and I vehemently disagree. I grew up on a rural acreage a half mile from my grandfathers farm. Between home and the farm I was constantly exposed to all the allergens someone can be exposed to - horses, cows, cats, dogs, pollen, you name it, I spent a bunch of time with it starting from birth. I was and still am allergic to all of it.

People did and do wear clothing that covers all of their skin when outside for any period of time.

Clothing. Part of the issue is we have a bikini-body culture and the money to spend on sunscreen.

But if you look at people who spend a lot of time in the sun professionally, they rely on long sleeve shirts and pants to protect themselves.

> But if you look at people who spend a lot of time in the sun professionally, they rely on long sleeve shirts and pants to protect themselves.

And hats!

Aye, I don't wear sunscreen as it tends to irritate my skin. Long sleeves and pants do the job just fine, usually; but the fabric matters! Ie, a thin cotton T will provide a little protection, but you'll still get burned eventually.

I got a big floppy sun hat like you see the ultra-runners or toddlers at the beach wearing. I look like a dork but I can take the kids out all day riding bikes, fishing, playground and don't need sunscreen.

I still sunscreen the kids because they take their hats off all the time.

Without going too far back in time, let's say until the 1970's, everyone and particularly people more exposed to sun - tyically peasants, farmers, fishermen and similar - would have been fully clothed (long sleeve shirts, long trousers) and would always, and I mean always, wear a hat when outdoors.

The whole idea of sun bathing is as well relatively recent, I believe going back to the early years of the past century and was anyway limited to very few.

And, as anecdata only - in the '70's - I was a child/kid and when we went to the seaside there were a few rules (carved in stone) by my granny:

1) you get to the beach no later than 8:00

2) you get out of the beach no later than 11:00

3) you can optionally go back to the beach no earlier than 16:00

4) for the first 15 days of holidays you stay under the tent/umbrella at all times except when taking a bath

Neatly avoids peak UV hours, certainly.

Mankind made it a long way without antiseptics, antibiotics, or electricity. I'm not sure what your point is.

People didn't travel to sunny areas every summer to sun bath, I don't think sun bathing was even considered an enjoyable activity until very recently.

Mankind evolved locally to handle sun, the problem is when your average pale as fuck northerner decides to go to Mallorca for 2 weeks in July

Surviving is a low bar

The article title is misleading.

A non misleading title would be: “common sunscreen chemical filters may become more toxic when zinc oxide is present”

The paper was evaluating the effect of zinc oxide on these chemicals: > Octisalate (INCI: Octyl salicylate; CAS: 118-60-5) was purchased from TCI Chemicals. DHHB (INCI: Diethylamino hydroxybenzoyl hexyl benzoate; CAS: 302776-68-7; received as UVINUL® A PLUS) and Bisoctrizole (INCI: Methylene bis-benzotriazolyl tetramethylbutylphenol; CAS: 103597-45-1; received as TINOSORB® M, a 50% aqueous suspension of the UV-filter)

And also solvated them in DMSO, while being hand wavy about the potential interactions of dmso like functioning as a carrier agent, instead claiming because dmso is safe for the fish in isolation it won’t change the study… their study is claiming evaluating things in isolation is misleading and yet they do exactly that. Ughhhh

And I’m not an animal chemical effect specialist, but are zebra fish embryos really that representative of human skin exposure?

That said, further analysis does need done on mixed sunscreens. Even though I think this paper has issues, hopefully it spurs more and better research. And it does show that mixed sunscreen chemicals may cause more degradation of the organic components, so that definitely needs follow up studies.

I'm not paranoid about using sunscreen, but it seems pretty obvious to me that slathering chemicals all over my skin and baking in direct sunlight for an extended period of time should be avoided.

I've found that bringing a decent umbrella and wearing a big hat helps a ton, and just generally trying to stay in the shade. That and just reasonably limiting exposure alternating between swimming and relaxing in the shade.

I hate the greasy feeling of sunscreen but I’ve yet to find a non greasy one that survives sweating.

I’ve pretty much given up on sunscreen. I wear at hat that covers my face and neck. And a long sleeve swim shirt when doing out door activities or swimming.

The paper: https://link.springer.com/article/10.1007/s43630-021-00101-2

…says a single study, which the headline makes clear, but the HN submission title elides.

Solumbra makes good sun protective clothing.

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